It is well known that solid titanium catalyst component with magnesium, titanium, halogen and electron donor as basic compositions can be used in the polymerization of olefin CH2═CHR, especially in the polymerization of alpha-olefins having 3 or more carbon atoms, higher isotactic polymer can be obtained in higher yield. An electron donor (ED) compound is one of indispensable compositions of catalyst component, and with the development of internal ED compound, polyolefin catalyst is continuously renovated.
At present, a large number of various ED compounds have been disclosed, for instance, polycarboxylic acids, monocarboxylic esters or polycarboxylic esters, anhydrides, ketones, monoethers or polyethers, alcohols, amines, and their derivatives, among of which aromatic dicarboxylic esters, such as di-n-butyl phthalate or diisobutyl phthalate (cf. CN85100997A), are commonly used. See also EP 0045977 (phthalates); CN1042547A, EP0361493, EP0728724 (1,3-diether compounds); CN1054139A, CN1105671A (1,3-diketone compounds); CN1236732, CN1236733, CN1236734, CN1292800 (specific substituted malonates), PCT International Application WO 0063261 (succinates), PCT International Application WO0055215 (β-substituted glutarates), CN1242780 (cyano-esters), CN1087918 (diamines), PCT International Application W003022894 (maleates), CN1436766A, CN1436796A (a specific kind of polyol esters) for ED compounds.
However, the catalysts disclosed in above-mentioned publications have some disadvantages in use of olefin polymerization. The present inventors have surprisingly found that catalysts for olefin polymerization exhibiting excellent general performance can be obtained by using a novel dibasic ester compound as internal ED. When used in propylene polymerization, the catalysts exhibit satisfied polymerization activity and good hydrogen response, and the resulting polymers have higher stereoselectivity and broader molecular weight distribution (MWD). These properties are desired in the development of different grades of polymers.
In addition, in the prior art, one approach commonly used to improve general performance of catalysts is to use more than one ED compounds in the preparation of the catalysts. For instance, CN1268957A discloses the use of two ED compounds in the preparation of catalysts, wherein one ED compound is selected from the group consisting of ether compounds containing two or more ether bonds, and the other is selected from the group consisting of ester compounds of monocarboxylic acids or polycarboxylic acids. The prepared catalysts exhibit higher polymerization activity, and the resultant polypropylene resins have higher content of insolubles in xylene and lower crystallinity, so that the polymers are suitable to prepare bi-oriented polypropylene film (BOPP). For another example, WO03/002617 proposes to add at first a minor amount of monofuntional compound, for example ethyl benzoate, followed by the addition of another ED compound in the preparation of a catalyst. Although the obtained catalyst contains little or undetectable said monofuntional compound, it exhibits improved catalytic activity and melt flow index property. Although the properties of the catalysts are improved by these methods in some extent, the catalysts are still unsatisfactory in terms of MWD of the polymers.
The present inventors have found that catalyst components and catalysts exhibiting excellent general performance can be obtained by using said dibasic ester compound and a 1,3-diether compound or a phthalate ester compound as internal ED in the catalyst for olefin polymerization. When used in olefin polymerization, especially in propylene polymerization, the catalysts exhibit higher polymerization activity, and the resulting polymers have broader MWD.